Fingers, four.
[UPDATED for 10.5.8]
It’s quite simple actually, just grab this file (AppleUSBMultitouch.kext), open a terminal window and type this:
sudo mv /System/Library/Extensions/AppleUSBMultitouch.kext /System/Library/Extensions/AppleUSBMultitouch.old
that will backup your current multitouch driver, and next we’re gonna install the new one:
sudo mv ~/Downloads/AppleUSBMultitouch.kext /System/Library/Extensions/
( you can also copy it there using finder )
Final step is to repair permissions, use Disk Utility, select your Macintosh HD and click “repair permissions”, when it’s over reboot and voilà!
